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# Logic Path Timing by Partial Path Calculation

IP.com Disclosure Number: IPCOM000049321D
Original Publication Date: 1982-Apr-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 2 page(s) / 57K

IBM

## Related People

Hitchcock, RB: AUTHOR [+4]

## Abstract

The normal logic path analysis is performed by drawing the logic path and the associated data and clock propagations to each of the latch (or capturing) elements. Fig. 1 shows two paths from one input to two different latches (L4 and L5). The normal path analysis calculations are shown. As can be seen, one path makes it in the required time (L5) and the other one does not (L4). These calculations are performed in the regular manner and on a per path basis.

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Logic Path Timing by Partial Path Calculation

The normal logic path analysis is performed by drawing the logic path and the associated data and clock propagations to each of the latch (or capturing) elements. Fig. 1 shows two paths from one input to two different latches (L4 and L5). The normal path analysis calculations are shown. As can be seen, one path makes it in the required time (L5) and the other one does not (L4). These calculations are performed in the regular manner and on a per path basis.

Fig. 2 shows the same logic diagram but with a single latch to single latch path calculation. It is simpler to perform these latch to latch calculations than the total path calculation. The problem is how to combine the small path calculations to achieve an accurate total path result. In Fig. 2, a table shows how to derive the total path value from the latch to latch paths. The procedure is as follows: 1. Create a Running Time Table with:

One column for latch to latch path description

One column for the spare time of data to the latch

One column for this running time

Each latch to latch path is described by one row.

2. Spare Time Calculation:

Clock Leading Edge Time - Data Arrival Time = Spare Time

Spare time can be negative (possible problem) or positive

(no problem).

Data arrival time is the propagation time from latch output

to next latch input.

3. Running Time Calculation:

Previous Row Running Time + Spare Time = Current Row

Running Time

Previous Row Running Tim...